Optical: systems and elements – Projection screen
Reexamination Certificate
1999-09-03
2001-05-29
Adams, Russell (Department: 2851)
Optical: systems and elements
Projection screen
C359S453000, C359S456000, C359S457000, C359S460000, C359S506000, C359S493010
Reexamination Certificate
active
06239907
ABSTRACT:
BACKGROUND
This invention relates generally to transmissive screens, and more particularly to transmissive screens suitable for use in rear projection systems.
Rear projection screens are generally designed to transmit an image projected onto the rear of the screen into a viewing space. The viewing space of the projection system may be relatively large (e.g., rear projection televisions), or relatively small (e.g., rear projection data monitors). The performance of a rear projection screen can be described in terms of various characteristics of the screen. Typical screen characteristics used to describe a screen's performance include gain, viewing angle, resolution, contrast, the presence of undesirable artifacts such as color and speckle, and the like. It is generally desirable to have a rear projection screen that has high resolution, high contrast and a large gain. It is also desirable that the screen spread the light over a large viewing space. Unfortunately, as is described more fully below, as one screen characteristic is improved, one or more other screen characteristics often degrade. For example, in order to increase the screen gain using the same overall structure, one must decrease the viewing angle over which the screen is readily observable. As a result, certain tradeoffs are made in screen characteristics and performance in order to produce a screen that has overall acceptable performance for the particular rear projection display application.
Thus, there remains a need for screens that have improved overall performance while meeting the minimum performance criteria necessary for the rear projection display application in which the screen is used.
SUMMARY
Generally, the present invention relates to a dispersing element for a rear projection screen assembly that is sensitive to the polarization of the light passing through the element. In particular, the element disperses light having a first polarization differently from dispersing light having a second polarization orthogonal to the first polarization. The dispersing element may be aligned with a polarization axis neither parallel nor perpendicular to the polarization of the light passing through the element. The dispersing element may also be employed with a polarizer to remove unwanted light that propagates through the dispersing element. The dispersing element may also be rotatably mounted relative to a polarized light source so as to vary the angle between the polarization axis of the element and the polarization direction of the light.
In one embodiment, a rear projection system includes a light source that projects light having a polarization parallel to a source polarization direction. A transmission screen is disposed to receive light from the light source, and has a first scattering layer with a first scattering distribution for light having a polarization parallel to a first screen polarization axis and a second scattering distribution for light having a polarization parallel to a second screen polarization axis orthogonal to the first polarization axis. The angle between the first polarization axis and the source polarization direction is selected to be greater than 0° and less than 90°.
In another embodiment, a rear projection system has a light source that projects light having a polarization parallel to a source polarization direction. A transmission screen is disposed to receive light from the light source. The transmission screen includes a first scattering layer with a first scattering distribution for light having a polarization parallel to a first screen polarization axis and a second scattering distribution for light having a polarization parallel to a second screen polarization axis orthogonal to the first polarization axis. The transmission screen also includes a polarizing layer oriented to transmit light polarized parallel to the source polarization direction, and to prohibit transmission of light polarized perpendicular to the source polarization direction.
In another embodiment, a display device includes a light source that projects light having a polarization parallel to a source polarization direction. A transmission screen is disposed to receive light from the light source. The transmission screen has a first scattering layer with a first scattering distribution for light having a polarization parallel to a first screen polarization axis and has a second scattering distribution for light having a polarization parallel to a second screen polarization axis orthogonal to the first scattering axis. The first scattering layer is rotatably mounted in the display device. Rotation of the first scattering layer results in a variation of an angle between the first polarization axis and the source polarization direction.
In some embodiments, the light source is an image light source that projects an image of polarized light towards the transmission screen.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments.
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Allen Richard C.
Chang Jeffrey C.
Merrill William W.
Moshrefzadeh Robert S.
Weber Michael F.
3M Innovative Properties Company
Adams Russell
Cruz Magda
Miller William D.
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